Some methods of installation require drilling out the center hole in the truck bolster. On the SP trucks in particular [P11J, P21 models], it is recommended that trucks be constrained by holding the end sills rather than the sides, as the SP brake cylinders are somewhat fragile.
Installation-AHM, Con-Cor, CV snap-on
The truck bolsters have a mounting hole in the center, originally designed to accept the Central Valley snap-on kingpin. A larger off-center mounting hole is designed to accept the kingpin for Con-Cor and AHM passenger cars.
Installation - Brass
For mounting on brass cars, the center hole may need to be drilled out to accept the truck mounting hardware. Or you may wish to re-design the truck mounting so that trucks can be removed without having to remove the car floor.
Installation-Walthers LW cars
For Walthers new streamlined cars, it will be necessary to either modify Walthers kingpin or enlarge and countersink the center hole in our truck to attain the correct car height. A couple of ideas for doing this are shown in the above sketches. Make sure the car sits level with the track and the trucks swivel freely when finished. Note: drilled holes may need to be slightly larger than shown.